BRUSSELS — Airlines canceled hundreds of flights across Europe and added hours to trans-Atlantic journeys Sunday as planes were diverted around a large plume of ash spewed by an Icelandic volcano and stretching from Greenland to Portugal.

So far, the weekend cancellations have been a fraction of the flights nixed two weeks ago when jittery European air traffic authorities closed down much of the continent's airspace for fear the volcano's abrasive ash could harm jet engines. But the possibility loomed of continuing eruption, and rising costs to airlines from ongoing disruption.

The bulk of the cloud, measuring 2,100 miles long and 1,400 miles wide (3,400 kilometers by 2,200 kilometers), stretched over the North Atlantic, according to the Irish Aviation Authority. It ordered Ireland's five westernmost airports to close Sunday afternoon but allowed the country's three biggest airports in Dublin, Shannon and Cork to stay open.

Airlines diverted their trans-Atlantic traffic north and south of the cloud, causing congestion as planes tried to squeeze through remaining routes. Some connections were canceled entirely because of an offshoot of the main cloud that was snaking its way from Portugal through Spain, southern France and northern Italy, then up to Germany, the Czech Republic and Austria.

Eurocontrol, the Brussels-based agency that coordinates air traffic control centers throughout the continent, warned airlines to plan on taking on more fuel for the longer flight around the North Atlantic no-fly zone.

It said there would be approximately 24,500 flights within the European area Sunday, about 500 below average for this time of year. It said the ash cloud hovering over the continent was expected to dissipate and that most of the closed airports were likely to reopen later Sunday.

Daniel Gerstgrasser, a meteorologist with Switzerland's national weather agency, said rain would help wash out the cloud by Monday morning and no further ash drifts were expected to reach the continent in the coming 24 hours.

Longer-term forecasts were less clear. Meteorologists say that until Eyjafjallajokul (pronounced ay-yah-FYAH-lah-yer-kuhl), the volcano in southern Iceland, stops erupting, the future course of Europe's ash crisis will depend heavily on the prevailing winds. The eruption of the glacier-capped volcano has shown no signs of stopping since it began belching ash April 13. It last erupted from 1821 to 1823.

Irish airline Aer Lingus apologized to its customers for a string of flight cancellations since Tuesday, when the ash threat returned to Irish air space after a two-week break. Its trans-Atlantic services to Boston and New York were operating Sunday subject to delays.

United Airlines canceled four flights from Rome, Geneva and Zurich to Chicago and Washington. Other trans-Atlantic flights were operating with an average delay of two hours, said spokeswoman Megan McCarthy.

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European carriers including British Airways, Germany's Lufthansa and Air France reported delays but no cancellations on trans-Atlantic flights.

Budget airline easyJet stopped all connections to and from its hub in Geneva while Portuguese airports reported 223 cancelations at Porto and Lisbon. Like many airlines, easyJet was using the short messaging platform Twitter to update passengers on the latest developments.

Air space in northern Italian was closed for six hours Sunday, and although Milan's two airports were among those coming under the no-fly zone, other airports heavily used by tourists and Italians for weekend trips, such as Rome' airports and Venice's Marco Polo airport, remained open.

Alitalia said Milan's Malpensa airport quickly geared up to resume flights to New York, Tokyo and Moscow. It said the great majority of passengers who couldn't fly out during the six-hour shutdown would be accommodated on flights later on Sunday.

Iberia canceled some flights to Germany and to and from regional airports in the north of the country including Bilbao, Valladolid, Salamanca and Burgos.

Switzerland's national carrier canceled one trans-Atlantic route from Zurich to Washington and 21 others to destinations in Europe because of airport closures in Italy and Germany.

"There will definitely be additional costs" to airlines because of the latest disruptions, said Swiss spokesman Jean-Claude Donzel. So far however, the airline has no plans to pass these on to customers, he said.

Scandinavian operator SAS, which is headquartered in Stockholm, canceled four European flights. Spokesman Bertil Ternert said the company normally has around 700 flights on Sundays and therefore the financial impact would only be marginal.

Last month's travel chaos — which lasted five days, saw much of European airspace closed and the cancellation of over 100,000 flights — stranded passengers around the world and caused airlines direct losses of more than euro1 billion ($1.3 billion).

Lekic reported from Brussels. Associated Press Writers around Europe contributed to this report.

Video: More delays

Closed captioning of: More delays

>>>developing now that volcano in iceland is once again wreaking havoc on airports and is forcing
transatlantic flights
to change their routes in order to avoid a massive no-fly zone.
nbc
's
jim
maceda is in london for us.
jim
, here we go again. where are the worst delays and how long will they last?

>>reporter: that's right,
alex
, here we go again and it's what the experts warned us about even a month after that icelandic volcano started spewing that mix of steam and ash. worst hit so far is
italy
where airports in the
northern part
of that
country
are closed at least until
later today
. also the northwestern part of spanish airspace was closed but it's starting to reopen now and
portugal
's second largest hub shut until midday portuguese time with major delays and cancellations. in france 30 flights from paris to
southern europe
canceled. it appears french domestic flights are flying normally. here in
london heathrow
and also the
frankfurt international airport
, the major hubs in
europe
, reported minimal delays but the bad news is winds are expected to spread that
ash cloud
which is now being seen from
ground level
to 20,000 feet all the
way across
into
eastern europe
so it's very hard to say how long these currents or future disruptions will last. as you said,
alex
, the
transatlantic flights
are flying and they are being diverted over green land. what that means they're taking on more fuel to fly around the no-fly zone and that means those flight times will be longer as well. if there's good news it's that these disruptions, as we both know, pale next to what we reported last month. that five-day shut down that saw 100,000 cancellations, almost $2
billion
of losses to the airlines. but this type of disruption,
low level
as it may seem, is annoying. it can wreak havoc and it's going to go on according to the experts possibly for months. back to you.

>>well, people are still talking about their stories from those five days. that's for sure.